The installed base of mobile phones and other portable computing devices grows in sheer number and computational power each day. Virtually ubiquitous and deeply entrenched in the lifestyles of people around the world, mobile devices transcend nearly every cultural and economic barrier. Computationally, modem mobile phones may offer speed and storage capabilities comparable to desktop computers of just a few years before, enabling on-demand sound synthesis and other musical applications. As a result, some modem mobile phones including smartphones, may support basic playback of audio and video.
However, mobile device platforms, networks, application execution environments, and sheer volume of content still impose significant practical limitations on application developers' abilities to deliver compelling user experiences with audiovisual entertainment to users of mobile devices. Playback customization options may be limited, such as to manual adjustments of playback settings for an entire content instance at a time. Other content instances may be alternated or interposed only between entire content instances, or at predetermined breakpoints that may disrupt natural flow of playback.
An instance of content for playback, such as a video or audio file of a song recording or a backing track for the song, may not have any way to differentiate structural elements of the song, such as music theoretic concepts of verse, chorus, bridge, hook, etc., and their structural boundaries within the song. Without awareness of such structural boundaries within content instances, playback options, such as for customization and interposition of other content, are limited and lack granularity.